Currently, a freight car generally includes a car body, a bogie, a brake rigging, a coupler draft gear, etc. The bogie is used for supporting the car body, guiding the freight car to run along rails, and bearing various loads from the car body and the rails. The most common bogie in the railway freight car is a three-piece two-axle bogie, which includes a bolster, two side frames, two wheel sets, a spring damper device and a brake rigging.
However, the anti-lozenge-distortion rigidity of the three-piece two-axle bogie is low, and the critical speed during curve negotiation is not high. Aiming at the above disadvantages of the three-piece two-axle bogie, a cross-braced type three-piece two-axle bogie is commonly adopted. An elastic crossing rod connection is additionally arranged between two side frames of this cross-braced type three-piece two-axle bogie, thereby increasing the capability of resisting displacement between the two side frames, and improving the anti-lozenge-distortion rigidity of the bogie. Currently, a central cross-braced type three-piece two-axle bogie is mainly applied in the freight car. FIG. 1 is a top view of the central cross-braced type three-piece two-axle bogie in the prior art. As shown in FIG. 1, the bogie comprises wheel sets, side frames, a bolster, a spring damper device, a brake rigging, a spring, an adapter, a cross-braced device and the like, wherein ‘X’-shaped two connecting rods pass through preset holes in the middle of the abdominal region of the bolster, two ends of each connecting rod are connected with the two side frames to form a connecting rod mechanism, and two ends of each side frame are supported on the wheel sets by an journal box rubber pad and the adapter. A pair of connecting rods are arranged between the two side frames, thus improving the anti-lozenge-distortion rigidity of the bogie as well as the dynamic performance of the car.
FIG. 2 is a three-dimensional structural schematic diagram of the bolster of the central cross-braced type three-piece two-axle bogie in the prior art, and FIG. 3 is a cross-section schematic diagram of the middle part of the bolster of the central cross-braced type three-piece two-axle bogie in the prior art. As shown in FIG. 2 and FIG. 3, the two connecting rods pass through the abdominal cavity of the bolster and intersected at the middle part of the abdominal cavity, so that the middle part of the bolster is a cavity. During the running of the bogie carrying the freight car body, the bolster mainly bears the vertical load applied to a center plate. The vertical load only can be transferred by side walls since the middle part of the bolster is a cavity, and the strength of the bolster for bearing the vertical load is very weak. Therefore, in order to guarantee the strength of the bolster for bearing the vertical load, the thicknesses of the side walls in the middle part of the bolster need to be increased, so that the weight of the bolster is largely increased, accordingly the whole weight of the freight car is increased, and the effective load of the freight car is reduced.